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(NECN: Scot Yount, Arlington, Mass.) - The rain pours down and it has to go somewhere. The upper Mystic Lake dam is just one of 39 dams around the commonwealth that engineers are keeping a close eye on.
Rick Sullivan/Commissioner DCR: "And we have over 30 inspectors on the ground making those very regular inspections, they are coming in literally every hour."
That's because a number of these dams are classified as high hazard, meaning if they failed it could be catastrophic.
Rick Sullivan/Commissioner DCR: "We have people obviously that live downstream, so that's there a potential if there is a catastrophic event you would have a personal injury or loss of life that could possibly happen."
Upper Mystic Lake Dam in Arlington, Massachusetts is being reconstructed, a five million dollar project is underway.
Rick Sullivan/Commissioner DCR: "The condition of that dam was obviously poor, so it rated at the top of the list in terms of the ones that needed to be replaced."
Ian Bowles/Secretary of Energy and Environmental Affairs: "The reconfigured structure will give us greater management control of it, we will be able to raise and lower the dam and also will add a fish passage which has been an area where fish bump up against the dam and can't come up through the upper Mystic Lakes."
But right now the pressure on the old dam and a kind of temporary dam called a coffer is immense.
Let me give you some sense of what you are looking at right here, this water flowing out of here is four thousand gallons a second, and it is being held back by this timber dam, that means it's made of wood, and that dam was built during the Civil War.
Mike Galvin/Dam Engineer: "The dam is actually timber piles, so they were driven in the Civil War time and most of those are still pretty much intact."
However, there is no room for error. In all, the state oversees some 2900 dams many are private but must be inspected too. A big job that has gotten more critical as with every raindrop.